Integrated circuits are used in transponders that are either passive transponders or semi-passive transponders or back-scattering transponders. Any transponder of these types can comprise one or more rectifiers that function as a power supply or as a detector. The transponders function as so-called contactless or wireless identification systems or as radio frequency identification systems in which the transmissions take place between one or several base stations or rather reading devices and one or several transponders. These transmissions transmit data in a wireless or contactless manner. The integrated circuits may comprise sensors, for example for measuring temperatures, whereby the transponders function as so-called remote sensors.
The transponder or rather its transmitter receiver sections normally do not comprise an active transmitter for the data transmission to a base station. These systems are referred to as inactive systems or as passive systems if they have no power supply of their own, or as semi-passive systems if they have their own power supply. In those instances where the data transmissions take place over distances clearly larger than 1 m and the wireless transmission takes place with ultra high frequencies or microwaves the transponder functions, as a rule as a so-called back-scatter or as a so-called back-scatter coupled device. For this purpose the base station emits electromagnetic carrier waves. These waves are modulated in the transponder, specifically in the transmitter and receiver portion of the transponder in accordance with the data to be transmitted to the base station and then reflected back to the base station. This modulation is performed normally by a variation of the input impedance of the receiver/transmitter portion of the transponder which causes a variation of the reflection characteristics of an antenna connected to the transponder.
Ever increasing demands are made on the transmission range of such transponders. In connection with passive transponders or remote sensors, the energy required to operate these devices is extracted from the electromagnetic field with the aid of an antenna as the field is emitted by the base station. For this purpose the rectifier is connected to the antenna for generating and operating voltage. The rectifier is conventionally constructed as a single stage or multi-stage voltage doubling circuit which contains rectifier diodes for performing the rectifying function. These diodes are generally Schottky-diodes when the rectifier functions in the operating frequency ranges in the UHF range or higher.
In the integrated circuit these Schottky-diodes comprise a reference potential terminal for connection to a reference potential, for example in connection with a CMOS operation or process. Additionally, these Schottky diodes comprise a first service terminal and a second service terminal, whereby the diode path is formed between the first and the second service terminals while a parasitic impedance exists between the reference terminal and the first service terminal.
The parasitic impedance, particularly its real component determined by the ohmic components, reduces the efficiency or effectiveness of the rectifier circuit because a substantial proportion of the received power is dissipated, among others, in the ohmic impedance portions. Furthermore, the parasitic impedance has generally a very disadvantageous Q-value due to the Ohmic impedance components. Thus, a mismatch is hard to reduce or eliminate even if matching networks are used.